This invention relates to prosthetic ligaments, and more particularly to a mechanical, modular prosthetic ligament.
Ligaments are flexible, fibrous cords or bands which join bones together and provide restraint to movement or articulation of one bone relative to another. With such movement, significant tensile forces are imposed on the ligaments and occasionally the result is a partial or complete rupture of the ligament. Attempts at repairing such ruptures by simply sewing the torn ends together are oftentimes not satisfactory because, among other things, many ligaments are not well vascularized and therefore do not heal by themselves. Frequently the geometry of the tear will not allow stable repair. This is often the case with severe damage to a ligament such as a complete rupture. Further, such a repaired ligament often does not afford the stability afforded by a healthy ligament and allows the bones being held together by the ligament to move in directions not normally allowed, causing either pain or undue wear on the bones, or both.
Other approaches which have been taken to correcting damaged ligaments include replacing the ligament with biological material (facia, tendon, other ligaments, etc.), with synthetic material ("ropes" made of various polymer compositions such as Gortex [registered trademark]), or with artificial prostheses known as ligament prostheses or prosthetic ligaments. The drawbacks of replacing a ligament with autograft biological material are that it is costly, risky, weakens the body part from which the substitute material is taken, and generally involves a long rehabilitation time. The use of allograft biological material (generally from a cadaver) carries additional risks of possible rejection, disease transmission (such as AIDS), as well as failure of the material due to processing. The principal drawback with the use of synthetic replacement material is that fatigue fracture generally occurs, involving the flaking off of parts of the synthetic material giving rise to particulate disease, and mechanical failure of the material.
As for the use of prosthetic ligaments, although they are generally designed to mimic the natural ligament through the use of flexible materials, they typically lack sufficient tensile strength, lack desired elasticity and flexibility, do not provide sufficient stability, and lack both durability and reliability.